This invention relates to controllers for electrically-actuated braking systems, such as those used to apply the brakes on towed vehicles (trailers) in response to commands from the towing vehicle. More particularly, the invention relates to a trigger point inertial sensor and electronic controller responsive to towing vehicle brake actuation and manual control signals to energize the towed vehicle brake-actuation components in a controlled manner.
Known electronic controllers for towed vehicles include systems which provide continuous or pulsing drive excitation to the electromagnetic brake shoe actuators located at the trailer wheels. Pulse drive controllers provide improved brake control over the relatively less complex continuous brake excitation controllers. Timer based drive controllers apply a predetermined gradually increasing brake excitation signal to the towed vehicle brakes during towing vehicle brake actuation. These signals typically increase from a minimum brake excitation level to a maximum brake excitation level in as little as two seconds. This rapid rise time makes soft braking virtually impossible. More sophisticated pulse drive controllers apply pulsing brake drive excitation current to the electromagnetic brake shoe actuators which is proportional in magnitude to control signals from a pendulum type or other such proportionally responsive inertial sensor in the towing vehicle, or manual control input signals. Such inertial sensor systems can generate so-called regenerative braking, wherein the towed vehicle braking initiated by the inertial sensor will be sustained or even increased until the inertial sensor experiences less deceleration, which cannot occur until the towed vehicle has been slowed very substantially. Thus, even though such inertial sensor type controllers represent a significant improvement over prior art controllers by providing a variable proportionally or representatively responsive brake control signal, it remains desirable to provide an electronic controller which overcomes the limitations and undesirable characteristics of heretofore known timer based electronic controllers without using a proportionally-responsive inertial sensor.
A difficulty encountered in providing effective timer based electronic controllers is providing optimum brake performance at different braking levels. These controllers are typically provided with a gain control which is manually adjusted to vary the magnitude of the brake excitation current applied to the electromagnetic brake components. The gain control is set by the operator to accommodate different trailer weights and each operator's desired brake system performance. Operators cannot set the gain for both hard (e.g., panic) and soft braking since each requires a different braking current characteristic for optimum performance. If the operator sets the gain of the electronic brake controller to a level which provides smooth braking at low level deceleration, the controller will not be set to an optimum level for hard braking. If the brake controllers are set to supply a brake excitation level which provides optimum panic braking performance, the brakes will be applied too hard for smooth low-level deceleration. Accordingly, operators who adjust the controller for optimum hard or soft braking will not have desirable braking under the other braking condition.
An operator may attempt to set a compromise level between optimum hard and soft braking. However, the brake excitation level required for optimum high-level deceleration (panic braking) can be up to 50% greater than that required for optimum low-level deceleration. Because of this disparity between the hard and soft braking levels, the compromise gain will not operate near the optimum level for either soft or panic braking. Any attempt to set a compromise gain level will provide less than ideal braking performance under both conditions (e.g., increased braking distances and time during panic braking conditions) because the brakes fade due to overheating and "hopping" and "jerking" will occur under low level deceleration. Although the towing vehicle brakes are capable of decelerating both the towed and towing vehicles when the towed vehicle brake controller operates at low gain settings, low gain settings of the towed vehicle brake controller during hard braking will cause the towing vehicle brakes to overheat and fade, producing longer stopping distances. Due to inherent characteristics of electric brake design, this difficulty is magnified at higher speeds and for greater trailer loads. Accordingly, it remains desirable to provide a timer brake controller with improved performance at different braking levels.